1. Technical Field
The present invention relates to an optical writing control device, an image forming apparatus, and a method of controlling an optical writing device.
2. Description of the Related Art
In recent years, there has been a trend to promote the digitization of information. Image processing apparatuses such as printers and facsimiles that are used to output digitized information and scanners used to digitize documents have become indispensable.
In many cases, such an image processing apparatus is configured as a multifunction peripheral that can be used as a printer, a facsimile, a scanner, and a copying machine by including an image capture function, an image forming function, a communication function, and the like.
Among such image processing apparatuses, an electro-photographic image forming apparatus is widely used to output digitized documents. The electro-photographic image forming apparatus exposes a photosensitive element to form an electrostatic latent image. Then, the apparatus develops the electrostatic latent image with developer such as toner to form a toner image. Finally, the apparatus transfers the toner image onto a piece of paper to output the paper.
For an electro-photographic image forming apparatus, a linear light source such as an LEDA (Light Emitting Diode Array) may be used. The LEDA includes a plurality of LEDs (Light Emitting Diodes), which are arranged in a line along a main scanning direction as a light source to expose the photosensitive element. In such a linear light source, the diodes are classified into certain number of groups, and each group is subject to emission control, such as time-division emission control.
By applying such time-division control, the apparatus can reduce electric power required to illuminate the diodes, compared to simultaneous control, which illuminates all diodes simultaneously. On the other hand, an exposure position for each diode varies along with rotation of the photosensitive element, since the plurality of diodes are arranged in parallel to the rotation axis of the photosensitive element.
In a conventional technology, it is known to reduce total illumination period of all LED elements within a half of one line cycle. Moreover, it is also known to shift image data to correct misalignment due to the time-division control.
A typical full-color image forming apparatus has a plurality of image forming units. For example, a full color image forming apparatus includes four image forming units for CMYK (Cyan, Magenta, Yellow and Black). Necessary exposure time is different because of the material of photoconductive drums, toners, etc. As a result, the illuminating cycle might become different for each color during in the time-division control. Such difference of exposure times causes misalignment between each of the colors. Therefore, there is a need to prevent misalignment in one image forming unit, and to prevent the misalignment in the plurality of image forming units, by the time-division control.